78o 



younger annual rings, the overgrowth edges have assumed a beautiful, 

 spiral form, rarely to be observed, and the nutrition of the trunk depends 

 on the comparatively slender wood layers of the last few years. The 

 process is shown in less striking form in all hollow trees, for example, often 

 in willows and poplars. In conifers, the rotting away of the trunk, as a 

 result of longitudinal wounds, is a less frequent case, because the wound 

 surface usually coats over with resin, or at least the parts of the wood 

 exposed become resinous. This self protection, after a longitudinal injury, 

 becomes most apparent in the gathering of resin, as Fig. 177 shows. 



Fig-. 177. Section of a tiunk of Picea vulgaris with the overgrowth of the resin 

 channels. The entire age of the tree is 70 years. The first resin tapping (a) took 

 place at the age of 50 years, the second (b) at 51, the third (c) at 62, and the fourth 

 (d) at 65 years. (After Dobner-Notabe.) 



The wounds resulting from the gathering of resin, in the form of strips 

 some centimeters broad and about 2 m. long, from which the bark has been 

 removed, do not die for some time. In spruce trees, R. Hartig found that 

 the turpentine flowed in drops from the resin canals, lying in the medullary 

 rays, soon after injury. Although a large amount of resin is accessible to 

 the wound, since the resin canals running vertically in the trunk are in open 

 connection with those of the medullary rays, yet the very fluid turpentine, 

 as a rule, ceases to flow after the first year. The turpentine becomes thicker 

 by the volatilization of the turpentine oil and the turning to resin (oxida- 



